The former Marine accused of killing Erin Corwin admitted searching the Internet about how to dispose of a body, and .22-caliber cartridge casings at the mine shaft where she was found matched those found in his Jeep and home, according to an arrest warrant filed in California Superior Court.

Christopher Brandon Lee also asked a witness about the best way to dispose of a body and told investigators he was collecting tires the morning Corwin disappeared. A tire and pieces of rebar also were found at the mine shaft.

A murder charge was filed Tuesday against Lee in Corwin’s death, according to the San Bernardino County District Attorney’s Office.

The DA’s office also filed a special circumstance allegation of “lying in wait,” increasing the potential penalty to life without parole, or death.

Lee, 24, was arrested in a traffic stop at 10 p.m. Sunday in Alaska — 30 minutes after Corwin’s body was identified by dental records.

He is due in court in Alaska at 3:30 p.m. Tuesday, for his initial hearing, according to the DA’s office.

If Lee waives extradition, he can be returned to San Bernardino County immediately. If he fights extradition, it may take four to six weeks.

“Once again, we are faced with a terrible crime that shows absolutely no regard for the value of human life,” San Bernardino County DA Michael Ramos said in a news statement. “Make no mistake that this office will fight to see that justice is carried out for our victim and her family.”

Corwin was found about 4:30 p.m. Saturday in a mine shaft 140 feet below ground by using video equipment. An urban search and rescue team recovered her body about 6:30 p.m. Sunday. The mine was a few miles southeast of Twentynine Palms, outside Joshua Tree National Park.

An autopsy confirmed Corwin was the victim of a homicide, but the cause of death was not released.

Investigators were still waiting for results to determine the 19-year-old was pregnant or not.

Her husband, Cpl. Jonathan Corwin, told investigators he last saw her June 28 and she was headed to Joshua Tree National Park. During the next seven weeks, authorities and volunteers searched 300 square miles. Specialized teams scoured more than 100 mine shafts and dove into multiple bodies of water.

Lee is a former Marine, originally from Anchorage, Alaska, who lived next to the Corwin couple at the Marine Corps Air Ground Combat Center in Twentynine Palms.

On July 21, The Desert Sun obtained court documents revealing that detectives believed Lee and Corwin were having an affair, and that Lee may have been the father of her possible unborn child.

According to these court documents, Corwin was scheduled to join Lee on a hunting trip on the day she disappeared.

Corwin told a friend that the trip was a “special day together,” planned to celebrate the fact that she was pregnant. However, detectives believed that Lee was afraid his wife, Nichole Lee, would discover the affair.

Nichole Lee is a “person of interest” in the investigation, according to San Bernardino County sheriff’s officials.

When questioned by detectives, Lee said he had kissed Corwin but that they never had sex. Lee also said he had gone hunting on the day Corwin disappeared, but that she wasn’t with him.

“It is highly likely that Erin could have been harmed by an unknown firearm,” the court documents state. “Sometime after Erin left with Lee, her phone was deactivated (turned off). Detectives believe if Erin was injured and left at an undisclosed location, she would not (be) able to call for help.”

In the weeks following Corwin’s disappearance, investigators served search warrants for Lee’s home and his Jeep. Authorities also searched a Yucca Valley horse farm, White Rock Horse Rescue Ranch, where the Lee couple stayed briefly in early July after Christopher Lee left the Marine Corps. The Lees and the Corwins volunteered at the ranch.

According to the court documents, Isabel Megli, owner of the horse ranch, told authorities that Nichole Lee had said detectives did not have a case “without a body,” and that they would “never find the body.”

While staying at the horse ranch in early July, Nichole Lee, supposedly told Megli that authorities “missed something” while searching Lee’s apartment, and that she was worried her husband did not have an alibi and would “not be able to keep his lies straight.”

Megli later told The Desert Sun that police had twisted her words in the court documents, taking her statements out of context in order to shift suspicion onto the Lee couple.

“They put a spin on it,” Megli told The Desert Sun. “I’m not going to say I didn’t say it, but it definitely wasn’t the whole of what I said.”

It was unclear Monday if Chris Lee has a lawyer. Nichole Lee could not be reached despite calls to her cell phone. Efforts to reach Lee relatives at their house in Anchorage were unsuccessful. The Desert Sun partnered with the Alaska Dispatch News in an effort to reach the family.